Heat treating strip material



Augu 2, 1966 (5.. A. TURNER, JR

HEAT TREATING STRIP MATERIAL Filed July 16, 1962 INVENTOR. CHARLES A. TURNER JR.

ATTORNEY.

United States Patent 3,264,143 HEAT TREATING STRIP MATERIAL Charles A. Turner, Jr., Flourtown, Pa., assignor to Selas Corporation of America, Dresher, Pa., a corporation of Pennsylvania Filed July 16, 1962, Ser. No. 209,872 7 Claims. (Ci. 148-11.5)

The present invention relates to the annealing of al-uminum, and more particularly to the continuous annealing of aluminum strip or wire.

Aluminum is annealed after cold working in order to recrystallize it and soften it for further working or forming into some desired shape. If a step can be incorporated in the annealing process which serves simultaneously to increase the yield strength without decreasing the ductility of the material, a much more desirable product will be produced.

It is an object of the present invention to provide a method and apparatus for the continuous, high speed annealing of aluminum strip or wire.

It is a further object of the invention to provide a series of operations to be performed on a continuously moving length of aluminum, in which it is annealed to produce a fine grain structure, while at the same time increasing the yield strength substantially beyond that which is usually obtained.

It is a further object of the invention to provide apparatus for the continuous treatment of a moving length of aluminum to improve its physical properties.

In practicing the invention, the strip or wire, which will be referred to below as strip, is moved through a path over suitable guide rolls while the strip is operated upon. The strip is first moved through a heating station, preferably in the form of open flame burners, where it is heated to annealing temperature. The material is then cooled in steps to a temperature slightly above ambient, and while at that temperature is stretched a few percent of its length. The treated material is then ready for forming or other work to be performed upon it. It is generally desirable to have the heating and at least the major portion of the cooling performed while the strip is moving vertically between a pair of guide rolls, so that the surfaces of the strip will not be scratched by any contact during this interval at elevated temperature wherein it is in a soft condition.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages and specific objects attained with its use, reference should be had to the accompanying drawing and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

The single figure of drawing shows diagrammatically apparatus which is used to carry out the applicants method.

Referring to the drawing, there is shown a strip of aluminum 1 which passes from a supply roll 2 through a path upon which work is performed on it to a take up roll 3. As the strip leaves the supply roll, it passes through a bridle roll 4, if a feed drive is required at this point, and around a series of guide rolls, including an upper guide roll 5 and a lower guide roll 6. Between 3,264,143 Patented August 2, 1966 these rolls the strip moves in a vertical pass, free of any contact, while it is being heated and cooled. Beyond roll 6, the strip is directed upwardly and then in a substantially horizontal direction to roll 3.

Heating of the strip is accomplished by a plurality of burners 7, which are prefer-ably of the type shown in Patent No. 2,228,114. These burners are of the open flame type in which flames of a uniform length are projected toward or against the strip from a burner that extends for a length equal at least to the width of the strip. Fuel is supplied to the burners in the form of a gas-air mixture through a pipe 8, with the supply of fuel being regulated by a valve 9. The strip is heated by the opposed burners firing directly against it and by the wash of hot gases and products of combustion that are produced from the burner. It is noted that heat baffles 11 are located a distance both above and below the burner station in order to protect roll 5 and the equipment which is located below the burners.

An initial retarded cooling is applied to the strip to lower its temperature from the annealing temperature to a temperature intermediate the annealing temperature and the final quench temperature.

The intermediate cooling is produced by supplying air in the form of jets equal to the width of the strip from air boxes 12 through nozzles 13 against opposite sides of the strip. The air is supplied under a suitable pressure in order to obtain the volume required to reduce the strip temperature to the desired value. The air is supplied through pipe 14, which is controlled by a valve 15. It is noted that the air jets directed against the strip are aligned on opposite sides thereof as are the burners '7. This arrangement keeps the strip from fluttering, and insures that it will travel vertically without engaging any of the apparatus on its opposite sides.

Immediately after the air jets, the strip moves into a quench tank 1d that is filled with a quenching fluid, such as water, to accelerate final cooling within the pass. It is noted that the guide roll 6 is located near the bottom of the tank, so that the strip will move vertically into the quenching liquid and be substantially cooled by that liquid before it is engaged by the roll. After passing around roll 6, the strip moves upwardly out of the tank and around a roll 17. Located over the tank and above thelevel of the quench liquid are a pair of wipers 18, which wipe the surplus water from the surface of the strip so that it will be dried by the time it reaches roll 17.

Immediately after leaving the quench tank and while the strip is at substantially the temperature of the quench liquid, it passes between pairs of bridle rolls 19 and 21. These rolls may be driven in any conventional manner, as by electric motors 22 anl 23, and they are so driven that rolls 21 rotate faster than rolls 19, so that the strip is stretched as it is moving between these rolls. When the strip leaves bridle rolls 21, it can be supplied directly to some forming apparatus or, as shown herein, can be coiled at 3 for storage and further use.

In the operation of the apparatus, strip to be treated is supplied continuously from coil 2 at a speed that will depend upon the equipment used, and which may be over 2.00 feet per minute. After leaving the coil, the strip passes through the bridle roll 4, if this is necessary, up over roll 5 and downwardly around roll 6 in the quench tank 16. As the strip moves vertically downward, it first passes between burners 7 to be heated to annealing temperature of from 800 F. to 1000 F. and preferably about 850 F. The strip is heated in a maximum of ten seconds and preferably in about 4 /2 seconds. Line speed is, in general, established by the desired production rate, and for a particular speed the annealing temperature is controlled by heat input. Varying conditions of strip speed and gauge are therefore accommodated by varying burner pressure (fuel) and number of burners. Adjustment of the fuel supply can be made automatically or manually by valve 9. Heating of the strip is helped by the wash of products of combustion along the strip surface between baffles 11. Annealed grain size is a function of the heating rate through the recrystallization temperature. Thus, this fast heating method accounts for a fine grain size for annealing temperatures over a wide range as noted above.

It has been found that immediate Water quenching of the strip from the annealing temperature will produce a waviness in the strip. Therefore, a preliminary retarded cooling is provided by the air jets 13. Sufficient air is blown through these jets, against opposite sides of the strip, to lower its temperature below 550 F. and preferably to about 525 F. When the strip temperature has been reduced to this value, it can be water quenched without rippling. Lower quench temperatures are avoided since they would extend the height of the pass line.

Immediately after passing between the air jets, the strip is moved into tank 16 to be water quench. The water is maintained at a temperature between 130 F. and 160 F., so that it will readily evaporate from the strip surface as it leaves the quench. The strip should travel through the quench water before it passes around roll 6 a sufficient distance for it to be reduced in temperature below 200 F., in order that steam will not be trapped between the roll and strip, since this will lead to the formation of wavy edges.

As the strip leaves the Water in the bath, it is approximately at the temperature of the water and preferably about 140 F. At this temperature, the strip will almost dry of its own accord. In order to insure that the strip will dry, however, and to avoid water stains on its surface, the strip passes between wipers 18 before going over roll 17 for removal of all excess water on the surface.

After being quenched, the strip passes between the pairs of bridle rolls 19 and 21 that are driven by suitable means, shown as motors, at such relative speeds that the strip is stretched between 1% and 6% and preferably about 4% of its length. This stretching can take place with the strip at any temperature between about 180 F. and ambient, but as not above, the strip will preferably be at about 140 F. Such stretching will have the effect of increasing the yield strength of the fine-grained material produced by the rapid heating and quenching to produce a strip with superior physical properties. The strip is then supplied direct to forming apparatus or coiled for storage until it is to be used.

As an example, 3003 aluminum alloy 0.020 inch thick, that has been batch annealed by ordinary methods requiring several hours for heating and soaking, has a yield strength of 6,000 p.s.i. and an ultimate strength of 16,000 p.s.i., with an elongation in 2 inches of 30%. After the same aluminum has been treated by the method of this invention, with a stretch of 4%, it has a yield strength of 15,300 p.s.i. and an ultimate strength of 19,400 p.s.i., with an elongation in 2 inches of 29.5%. Thus, the aluminum produced by the present process has improved yield strength with no appreciable loss in ductility. This upgrading of the inherent strength of the alloy by the present method also produces a fine grain, resulting from the rapid heating of only a few seconds, which results in smoother surfaces in a drawn product. Thus, buffing for final product finish is reduced or eliminated.

It will be seen that the method of this invention, using the relatively simple apparatus that is required, will produce continuously a superior product. The result is that the necessary strength required in a finished part can result utilizing an alloy of lower alloy content, or utilizing a lighter gauge strip of the same material, or utilizing the same gauge and alloy and gaining improved formability and strength.

While in accordance with the provisions of the statutes, I have illustrated and described the best form of embodiment of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit and scope of the invention set forth in the appended claims, and that in some cases certain features of my invention may be used to advantage with out a corresponding use of other features.

What is claimed is:

11. The method of continuously annealing non-heattreatable aluminum base alloys in strip form which comprises moving the strip downwardly between a pair of upper and lower guide rolls, at a first upper location between said rolls heating the strip by application of open flames to opposite sides thereof to a temperature within the range of 800 F. to 1000 F, at a second and lower location cooling the strip to below 550 F. by jets of air directed against opposite sides thereof, at a still lower point in the path of travel of the strip between said rolls quenching it in water to a temperature of less than 200 F, removing the strip from the Water, removing the water from the surface of the strip and stretching the strip between 1% and 6% as soon as it is removed from the quench water.

2. The method of continuously treating non-heattreatable aluminum base alloys in strip form which comprises moving the strip through a path including one after the other a heating station, a plurality of cooling stations and a Work station, heating the strip to annealing temperature in said heating station by the application of heat from an open flame, cooling said strip at a first cooling station by jets of air to an intermediate temperature of about 525 F., cooling the strip to about 140 F. at a second cooling station and stretching the strip about 4% at the work station, each of said operations on the strip being performed continually and in sequence as the strip moves through said stations.

3. The method of claim 2 in which the strip is moved in a vertical path from prior to said heating station until it is in the second cooling station.

4. The method of continuously treating non-heattreatable aluminum base alloys in strip form which comprises moving the strip through a path from a point of supply to a point beyond said path, at a first location in said path heating the strip to an annealing temperature of between 800 F. and 1000 F. by the application of flame and hot combustion products, at a second location in said path cooling said strip in steps to a temperature between not more than 200 F. and room temperature, the last cooling step including a water quench, drying the strip as it leaves the quench and continuously stretcting the strip lengthwise between 1% and 6%.

5. The method of treating non-heattreatable aluminum base alloys in strip form to upgrade its physical characteristics which comprises heating the strip from both its sides across its width with products of combustion to an nealing temperature, immediately cooling the strip to an intermediate temperature by a blast of air across its surface on both sides and then immersing the strip in a liquid bath maintained at a temperature below 160 F., removing the strip from the bath and while it is still substantially at bath temperature stretching the strip between 1% and 6%.

6. The method of treating non-heattreatable aluminum base alloys in strip form continuously which comprises moving the strip form a point of supply to a point of takeup through a path including a vertical portion, heating the strip at an upper location in said portion to annealing temperature by application to opposite sides of the strip of heat from individual burners directed toward the strip, cooling the strip to below 550 F. at a second lower location in said portion of said path by directing jets of air against opposite sides thereof, moving the strip at the bottom of said portion of said path into a quenching liquid to cool said strip to the temperature of the liquid, the strip being cooled to below 200 F. by the time it reaches the end of said portion of said path and, after the strip is moved from the quenching liquid, drying it and stretching it lengthwise continuously between 1% and 6%.

7. The method of treating non-heattreatable aluminum base alloys in strip form which comprises continuously heating the strip to annealing temperature, continuously cooling the strip continuously moving the cooled strip successively through two pair of bridle rolls, and driving said pairs of rolls at such relative rates of speed that the strip 20 is stretched between 1% and 6% by said pairs of rolls.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Alcoa Aluminum Handbook, 1957, pages 38-39.

DAVID L. RECK, Primary Examiner.

W. B. NOLL, H. F. SAITO, Assislanl Examiners. 

1. THE METHOD OF CONTINUOUSLY ANNEALING NON-HEATTREATABLE ALUMINUM BASE ALLOYS IN STRIP FORM WHICH COMPRISES MOVING THE STREIP DOWNWARDLY BETWEEN A PAIR OF UPPER AND LOWER GUIDE ROLLS, AT A FIRST UPPER LOCATION BETWEEN SAID ROOLS HEATING THE STRIP BY APPLICATION OF OPEN FRAMES, TO OPPOSITE SIDES THEREOF TO A TEMPERATURE WITHIN THE RANGE OF 800*F. TO 1000*F., AT A SECOND AND LOWER LOCATION COOLING THE STRIP TO BELOW 550*F. BY JETS OF AIR DIRECTED AGAINST OPPOSITE SIDES THEREOF, AT A STILL LOWER POINT IN THE PATH OF TRAVEL OF THE STRIP BETWEEN SAID ROLLS QUENCHING IT IN WATER TO A TEMPERATURE OF LESS THAN 200*F., REMOVING THE STRIP FROM THE WATER, REMOVING THE WATER FROM THE SURFACE OF THE STRIP AND STRETCHING THE STRIP BETWEEN 1% AND 6% AS SOON AS IT IS REMOVED FROM THE QUENCH WATER. 